Solid golf ball

ABSTRACT

Disclosed is a solid golf ball containing at least one rubber portion formed from a rubber composition comprising a base rubber, a co-crosslinking agent and an organic peroxide; an improvement being present in that the base rubber is a mixture of 
     (A) a solid polybutadiene rubber containing cis-1,4 bonds in an amount of at least 40%, and 
     (B) either a liquid polybutadiene rubber or a liquid isoprene-butadiene copolymer rubber, or both.

FIELD OF THE INVENTION

The present invention relates to a golf ball, particularly a one-piecesolid golf ball.

BACKGROUND OF THE INVENTION

Golf balls are classified into two types. One is thread wound golf ballswhich comprise a thread wound core and a cover covering the core, andthe other is solid golf balls, e.g. one-piece solid golf balls which areintegrally composed of rubber and two solid golf balls which arecomposed of a rubber core and a cover thereon.

The solid golf balls contain at least one rubber portion. The rubberportion has been prepared from a rubber composition which mainlycontains as base rubber butadiene rubber or a mixture of butadienerubber and the other rubber (e.g. natural rubber and isoprene rubber).The base rubbers, however, have some problems in processability (forexample, mixing process or extruding process), thus resulting in poorproduction efficiency. These problems are more serious when apolybutadiene having high Mooney viscosity or narrow molecular weightdistribution is used to improve the physical properties of golf balls.

SUMMARY OF THE INVENTION

The inventors have found that a rubber composition containing as a baserubber a mixture of a solid polybutadiene rubber and a specific liquidpolybutadiene rubber significantly improves the processability andsurprisingly enhances the physical properties of the resulting solidgolf balls (e.g. durability, impact resilience, hit feeling and thelike). Accordingly the present invention is directed to a solid golfball containing at least one rubber portion formed from a rubbercomposition comprising a base rubber, a co-crosslinking agent and anorganic peroxide; an improvement being present in that the base rubberis a mixture of

(A) a solid polybutadiene rubber containing cis-1,4 bonds in an amountof at least 40%, and

(B) either a liquid polybutadiene rubber or a liquid isoprene-butadienecopolymer rubber, or both.

DETAILED DESCRIPTION OF THE INVENTION

The polybutadiene rubber (A) employed in the present invention is solidat room temperature and contains cis-1,4-bonds in an amount of at least40%, preferably at least 80%. If the content of the cis-1,4 bonds isless than 40%, impact resilience is poor. Among the solid polybutadienerubber (A), it is preferred that the solid polybutadiene rubber (A) hasa high Mooney viscosity or a narrow or sharp molecular weightdistribution, especially a Mooney viscosity (ML₁₊₄ 100° C.) of 45 to 90or a ratio of weight average molecular weight/number average molecularweight (Mw/Mn) of 4.0 or less. The preferred solid polybutadiene (A)exhibits superior technical effects when combined with the liquid rubbercomponent (B). The polybutadiene (A) is commercially available in thetradenames of Ubepole BR 150 L or Ubepole BR 360L (both Ube Industries,Ltd.), BUNA CB 22 or BUNA CB 10 (both Bayer AG) and the like.

The rubber component (B) employed in the present invention is either aliquid polybutadiene rubber or a liquid isoprene-butadiene copolymerrubber, or both. The term "liquid" means that the rubber is flowable atroom temperature. The liquid rubber component (B) preferably has anumber average molecular weight of 1,000 to 50,000. Molecular weightsoutside the range deteriorate compression and impact resilience of theresulting golf balls or have poor processability. The liquidisoprene-butadiene copolymer rubber preferably contains at least 50% byweight of the butadiene component. If the isoprene component is morethan 50% by weight, crosslinking efficiency is poor and the physicalproperties of the obtained rubber are poor. The rubber component (B) iscommercially available, for example the liquid polybutadiene isavailable from Nippon Oil Co., Ltd. as Nisseki Polybutadiene B-3000 andthe liquid isoprene-butadiene copolymer rubber is available from KurarayCo., Ltd. as Kuraprene LIR-390.

In the base rubber, it is preferred that a weight ratio of thepolybutadiene component (A)/ the liquid rubber component (B) is withinthe range of 98/2 to 75/25, more preferably 95/5 to 80/20. If the liquidrubber component (B) is less than 2 parts, the technical effects of thepresent invention are not attained. If it is more than 25 parts, theobtained rubber composition is sticky and adversely makes processabilitypoor.

The base rubber of the present invention is mainly composed of the abovementioned two rubber components (A) and (B), but other diene rubbers,such as EPDM, styrenebutadiene rubber, polyisoprene rubber, naturalrubber and the like may be added thereto if necessary. The other dienerubber may be present in the base rubber in an amount of 40% by weightor less.

The co-crosslinking agent of the present invention can be unsaturatedcarboxylic acids or metal salts thereof. Examples of the unsaturatedcarboxylic acids and metal salts thereof are acrylic acid, methacrylicacid, and divalent metal salts thereof (e.g. zinc salts), and mixturesthereof. An amount of the co-crosslinking agent is within the range of15 to 60 parts by weight based on 100 parts by weight of the baserubber. The organic peroxide of the present invention can be anyonewhich is used in this field as polymerization initiator, includingdicumyl peroxide, 1,1-bis(t-butyl-peroxy)-3, 3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butylperoxide and thelike. Preferred is dicumyl peroxide. The organic peroxide may be presentin the rubber composition in an amount of 0.3 to 3.0 parts by weight,preferably 1.0 to 2.5 parts by weight based on 100 parts by weight ofthe base rubber.

The rubber composition of the present invention may further containfillers to control the specific gravity of the resulting golf balls.Typical examples of the fillers are zinc oxide, barium sulfate, calciumcarbonate silicate hydrate and the like. The rubber composition alsocontains antioxidants, chain transfer agents, stabilizers and the liketo enhance the performances of the resulting golf balls.

The rubber composition of the present invention can be prepared bymixing the above mentioned components, using a roll, a kneader, aBanbury mixer and the like. Mixing temperature and time are known in theart.

The solid golf balls of the present invention may be obtained byvulcanizing the rubber composition in a mold and optionally covering itwith a cover material (e.g. ionomer resin). Vulcanization may begenerally conducted at a temperature of 140° to 180° C. for 15 to 55minutes.

The rubber composition of the present invention can be easily processedor treated by mixing the polybutadiene rubber with the specific liquidrubber component (B). It is surprisingly that the golf balls obtainedfrom the rubber composition have excellent impact durability and hitfeeling.

EXAMPLES

The present invention is illustrated by the following Examples which,however, are not to be construed as limiting the present invention totheir details.

EXAMPLES 1-7 and COMPARATIVE EXAMPLES 1 and 2

A rubber composition was prepared from the ingredients shown in Table 1,using a kneader and a roller, and then vulcanized in a mold at 168° C.for 25 minutes to obtain a one-piece solid golf ball. The processabilityof the rubber composition was determined and the result is shown inTable 1.

The resulting golf ball was subjected to a measurement of physicalproperties (ball weight, compression, impact durability and hit feeling)and the results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Rubber composition                                                                           Examples                     Comp. Ex.                         (parts by weight)                                                                            1    2   3   4   5   6   7   1    2                            __________________________________________________________________________    Ubepol BR 150L*.sup.1                                                                        98   90  80  90  80  --  --  100  --                           Ubepol BR 360L*.sup.2                                                                        --   --  --  --  --  90  80  --   100                          Kuraprene LIR-390*.sup.3                                                                     2    10  20  --  --  10  20  --   --                           Nisseki Polybutadiene B-3000*.sup.4                                                          --   --  --  10  20  --  --  --   --                           Zinc oxide     25   25  25  25  25  25  25  25   25                           Methacrylic acid                                                                             25   25  25  25  25  25  25  25   25                           Dicumyl peroxide                                                                             1.0  1.0 1.0 1.0 1.0 1.0 1.0 1.0  1.0                          Antioxidant    0.15 0.15                                                                              0.15                                                                              0.15                                                                              0.15                                                                              0.15                                                                              0.15                                                                              0.15 0.15                         Processability*.sup.5                                                                        Good Very                                                                              Very                                                                              Very                                                                              Very                                                                              Very                                                                              Very                                                                              Poor Poor                                             good                                                                              good                                                                              good                                                                              good                                                                              good                                                                              good                                  Ball weight (g)                                                                              45.3 45.3                                                                              45.2                                                                              45.3                                                                               45.2                                                                             45.3                                                                              45.2                                                                              45.4 45.4                         Compression*.sup.6                                                                           100  101 100 98  97  102 101 100  101                          Impact durability*.sup.7                                                                     109  120 130 131 142 125 135 100  105                          Hit feeling*.sup.8                                                                           Normal                                                                             Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Good                                                                              Normal                                                                             Normal                       __________________________________________________________________________     *.sup.1 High cispolybutadiene rubber having a Mooney viscosity (ML.sub.1+     100° C.) of 43, a molecular weight distribution (Mw/Mn) of 2.8, a      sis1,4-bond of about 95% and a number average molecular weight of 210,000     available from Ube Industries, Ltd.                                           *.sup.2 High cispolybutadiene rubber having a Mooney viscosity (ML.sub.1+     100° C.) of 50, a molecular weight distribution (Mw/Mn) of 2.7, a      sis1,4-bond of about 95% and a number average molecular weight of 250,000     available from Ube Industries, Ltd.                                           *.sup.3 Isoprene-butadiene copolymer liquid rubber having a number averag     molecular weight of 35,000, and a butadiene content of 80% by weight,         available from Kuraray Co., Ltd.                                              *.sup.4 Liquid polybutadiene rubber having a number average molecular         weight of 3,000, available from Nippon Oil Co., Ltd.                          *.sup.5 Processability was evaluated with roll winding condition,             dispersibility of components, stock surface condition after rolling and       stock surface condition after rubberextruding. Very good: all items (i.e.     roll winding condition, dispersibility of components, stock surface           condition after rolling and stock surface condition after rubberextruding     is good. Good: Roll winding condition dispersibility of components and        stock surface condition after rolling are good, but stock surface is          slightly rough after rubberextruding. Poor: Roll winding condition is ver     poor when a rubber temperature is elevated. The surface after rubber          extruding is like pine cones even if it is extruded at low speed.             *.sup.6 Compression is determined by PGA rules. It is expressed as an         index when Comparative Example 1 is set 100. The larger is harder.            *.sup.7 A golf ball is repeatedly struck with an impact panel at a speed      of 45 m/s until the ball was broken out. Number of strikes is expressed a     an indes when that of Comparative Example 1 is 100. The larger the more       durable.                                                                      *.sup.8 An average of hit feeling with drivers of two men professional        golfers, one woman professional golfer and three top amateur golfers with     a handicap of 3 to 8.                                                    

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A solid golf ball containing at least one rubberportion formed from a rubber composition comprising a base rubber, aco-crosslinking agent and an organic peroxide; an improvement beingpresent in that said base rubber is a mixture of(A) a solidpolybutadiene rubber containing cis -1,4 bonds in an amount of at least40%, and having a Moooney viscosity (ML₁₊₄ 100° C. ) of .[.45.]..Iadd.43 .Iaddend.to 90 and a ratio of weight average molecularweight/number average molecular weight (Mx/Mn) of 4.0 or less; and (B)either a liquid polybutadiene rubber or a liquid isoprene-butadienecopolymer rubber, or both.
 2. The solid golf ball according to claim 1wherein said liquid rubber component (B) has a number average molecularweight of 1,000 to 50,000.
 3. The solid golf ball according to claim 1wherein said liquid rubber component (B) does not have carboxyl groupsat the terminals of the molecule.
 4. The solid golf ball according toclaim 1 wherein a weight ratio of polybutadiene component (A)/liquidrubber component (B) is within the range of 98/2 to 72/25.
 5. The solidgolf ball according to claim 1 wherein said co-crosslinking agent isacrylic acid, methacrylic acid or a divalent metal salt thereof.
 6. Thesolid golf ball according to claim 1 wherein an amount of theco-crosslinking agent is within in the range of 15 to 60 parts by weightbased on 100 parts by weight of the base rubber.
 7. The solid golf ballaccording to claim 1 wherein said organic peroxide includes dicumylperoxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2, 5-di(t-butylperoxy)hexane or di-t-butylperoxide.
 8. Thesolid golf ball according to claim 1 wherein said organic peroxide ispresent in the rubber composition in an amount of 0.3 to 3.0 parts byweight based on 100 parts by weight of the base rubber.